The present invention relates according to an aspect thereof to a method and device for controlling inactivation of a freewheeling function in a vehicle.
The present invention also relates according to further aspects thereof to a computer program, computer program product and a storage medium to be used with a computer for executing said method.
An automatic vehicle transmission designed from planetary gears usually has one-way couplings between the planetary gear steps, which, when a propulsion engine is in drive, lock in the automatic gear position for torque transmission from the engine to the drive wheels, but which, when torque is transmitted in the opposite direction, i.e. at zero throttle and with the vehicle in motion, disengage and cause the vehicle to freewheel without engine braking, which, by utilizing the kinetic energy of the vehicle, yields lower fuel consumption than if the engine is busy braking.
A corresponding freewheel function for automated mechanical transmissions (AMT) is shown in WO 2005/084995. Here, the freewheel function is automatically activated when a predetermined vehicle condition is prevailing. This condition comprises at least traveling in a not too steep downslope and that there is no fuel demand from the driver (via the accelerator pedal) or from a cruise control in the vehicle. When the freewheel function is activated with a certain vehicle set speed, i. e. during a time period when the cruise control is active, and a certain over speed limit (VBCC set speed) is exceeded, then the freewheel function is automatically inactivated and the vehicle is automatically braked to a speed under said VBCC setspeed—When vehicle speed is below VBCC setspeed the freewheel function will be activated again if the right vehicle conditions are still prevailing.
WO2005/084995 further discloses that said VBCC setspeed can be automatically adjusted in dependence of road gradient in the near future, e. g. in dependence of that the prevailing downhill slope will end in a near future, which means increased VBCC setspeed in order to postpone inactivation of the freewheel function.
FIG. 1 discloses activation and inactivation of a freewheeling function when traveling a moderate downhill which soon changes to a steeper (downwards position B) downhill. According to prior art (see FIG. 1) if vehicle travel resistance becomes less than zero (moderate downhill) said freewheeling function will be activated when the vehicle is in position A. If said moderate downhill changes to a steep downhill (position B and downwards) the vehicle will gain speed quickly and when said over speed limit (VBCC set speed) is exceeded at position C, the freewheel function will automatically be inactivated and the vehicle will be automatically braked (from position C and downwards) to a speed under said VBCC setspeed.
It is desirable to address a technical problem of how to further decrease fuel consumption in a vehicle equipped with such a freewheel functionality.
An aspect of the present invention involves inactivating said-freewheeling at the right vehicle position. This can be done by a method starting from when a freewheeling function in a vehicle is active due to a prevailing freewheeling condition. This method is according to an aspect of the invention characterized in the steps of:                predicting that said vehicle soon will travel in a steep downhill slope that is steeper compared to a prevailing downhill slope,        simulating if less fuel will be consumed if said freewheeling function is inactivated before said vehicle enters said steeper downhill slope compared to if said vehicle enters said steeper downhill slope with said freewheeling function active,        inactivating said freewheeling function before said vehicle enters said steeper downhill slope if said simulation shows that less fuel will be consumed.        
In one embodiment of the invention vehicle speed is starting to decrease before entering said steeper downhill slope and when inactivating said freewheeling function. In a further embodiment said inactivation of said freewheeling function comprises drivingly connecting a combustion engine to a transmission and driven wheels of said vehicle. In an even further embodiment of the invention said decrease of vehicle speed is performed by braking the vehicle with an engine braking device and/or an auxiliary braking device.
In another embodiment of the invention said simulation can also include simulating vehicle speed change with different possible gears engaged in said transmission and selecting the one gear that results in a smallest change of vehicle speed.
The device for controlling said automatic freewheeling relates to a vehicle that comprises an engine, an automated manual transmission, by said engine driven wheels, a freewheeling device and a control unit for controlling said engine, where said engine is arranged to drive said driven wheels via said automated manual transmission, and where said freewheeling device, said engine and said automated manual transmission are controlled by a control unit, where said control unit is arranged to perform the above method steps.